Taking batteries to the skies
A decade ago, I opened my seminar at Carnegie Mellon University comparing the curb weight of Tesla Roadster and Lotus Elise. Then, I made a now-obvious take that batteries would take the place of combustion reshaping the automotive industry, and thereby mechanical engineering. Now, it’s time to make a new bet: batteries will take to the skies! To realize electric future of aviation, I am moving to the University of Michigan, to be a part of the oldest Aerospace department in the world. Four transformative events have led to this move.
The first one begins in 2017, and as Gregory Barber later wrote in The Wired, “A few years ago, while driving on a stretch of interstate between Pittsburgh and San Francisco, Venkat Viswanathan began to feel a little existential. His trip was going smoothly — almost too smoothly, he thought. He would hum along for a few hundred miles at a time, stopping briefly for meals or to take in the early summer scenery. It was the classic Great American road trip. And it was hardly remarkable at all that he was doing it in an electric car.
Viswanathan, a scientist at Carnegie Mellon University, is an expert in high-energy-density batteries — designs that are meant to pack a lot of juice into not a lot of space. At times, this involves chemistry that can feel almost fanciful; the unobtanium of battery tech. But after that summer being propelled cross-country by a totally obtainable battery, he began to consider a different application for his work. “I was like, ‘Wait, what am I doing with all these new batteries I’m inventing?’” Viswanathan recalls. “Who is going to need them?” There was another way to travel coast-to-coast, he realized, one that batteries were far from decarbonizing: flight.”
Luckily, at the end of this trip, my collaborator and friend, Yet-Ming Chiang had just the assignment to address this existential angst: to work with Alan Epstein to understand the performance boundaries of hybrid and battery-powered aircraft. We would have two-hour long calls when we taught each other: batteries and aviation. This proved to be the start of an incredible collaboration.
In the summer of 2018, Geoffrey Bower, then at Airbus Vahana, now the “unfeasibly youthful Chief Engineer” at Archer, funded my first project on electric aviation. We jointly wrote one of the first papers identifying the performance needs of batteries for electric vertical take-off and landing aircraft, popularly called flying cars. We identified the “AND problem” of aviation batteries: the need to simultaneously have high specific energy to deliver long range and deliver high specific power at low state-of-charge for landing. Shashank Sripad later refined this leading to the definitive chart to assess the near-term feasibility and availability of eVTOL batteries for the specified mission.
Third transformative event happened when we tested our ARPA-E IOINCS lithium metal batteries, originally intended for EVs, on eVTOL missions and found compelling results to move forward in that direction. This work was recognized with MIT Technology Review Innovators Under 35. Sebastian Thrun took a bet and KittyHawk, joined as a commercial partner on an ARPA-E SCALEUP award, led by 24M Technologies. The focus is to build lithium metal batteries specifically for electric aviation, one of the largest federally funded programs to-date for aviation batteries, now with multiple commercial partners.
The final event almost didn’t happen. NASA and DOE jointly organized a workshop to understand battery needs for electric aviation. Dates clashed with planned travel, my wife asked me to reschedule and I am glad I did! Brian German and I led a breakout session where aerospace engineers identified battery requirements, and battery scientists identified suitable chemistries. Inspired by this breakout session, Alan Epstein and I assembled aerospace and battery dream teams to appraise what could be possible for battery-powered flight. In a perspective in Nature, we spelt out the gargantuan challenge ahead for large aircrafts, and identified a near-term target of around 1000 Wh/kg at the cell level, Bat1k as Halle Cheeseman would brand it that summer at the ARPA-E Summit.
Following this perspective and soul-searching conversations with Alan Epstein, John Langford, Charbel Farhat and Parviz Moin, I visited the top aerospace departments doing a seminar tour on my vision for electric aviation. I was excited by Anthony Waas’ ambitions for the future of aerospace at the University of Michigan and the incredible battery ecosystem in the Detroit area, led in large part by Mujeeb Ijaz.
What lies ahead? Aviation battery requires innovation at material and system levels. From our ARPA-E SCALEUP program, we spun out And Battery Aero Inc. with Shashank Sripad, to develop custom aviation battery systems from first-principles. Achieving the Bat1k challenge requires a radical departure from the current increment improvement rates. Three paradigm shifts that can enable Bat1k: (i) machine learning to rapidly downselect on battery materials. Aionics Inc, a company, Austin Sendek and I co-founded, will emerge as a dominant force in catalyzing this. (ii) robotic experimentation that allows testing “night and day, rain or shine” as Christopher de Bellaigue writes in Flying Green. Our electrolyte robot, Clio, represents the ChatGPT moment for battery materials innovation enabled by autonomous experimentation. (iii) advanced table-top characterization that will allow us to watch what happens inside the battery while it is happening.
Is electric aviation imminent? Alan Epstein enlightened me that in 1884, La France air ship completed a controlled round-trip flight, powered by a zinc-chloride battery, and it was “only a question of time and money” for electric aviation to take-off. However, by 1920, fuelled aircraft carried 12 passengers 800 km, and electric propulsion disappeared. A century later, it remains “a question of time and money”, but things are different this time. I made a bet with Akshat Rathi that I’d take an “air taxi” ride before I turn 40, a bet I expect to win easily. Soon after, with the battery advances discussed above, we could fly the 1920 mission all-electric.
